Rightly pointed by Dan, it's an issue with the Coordinate System - Coordinate Values mismatch.

WGS_84_Web_Mercator (Auxiliary Sphere) is a Projected Coordinate System. Thus, its units are in Meters. When you add the values (in Decimal Degrees) using Web_Mercator, it considers the units to be in Meters, instead of Decimal Degrees.

Here is what you need to do (**choose any one** of the following).

1. While using **Calculate Geometry** for calculating Centroid, you can **keep the default units**, i.e., don't change the units to decimal degrees. Then the values will be correct when you add data in WGS_84_Web_Mercator (Auxiliary Sphere).

2. If you want the **XY values in Decimal Degrees** (Calculate Geometry), then choose the Spatial Reference as **GCS_WGS_1984** while Adding XY Data (as pointed by Dan).

3. If you have **ArcGIS Desktop Advanced License**, you could use **Feature To Point**—Help | ArcGIS Desktop.

**Think Location**